DESCRIPTION (Investigator's Abstract): The proposal consists of three sets of experiments that use recent developments in the control of laser light to measure factors that limit spatial contrast sensitivity in the primate visual system: 1) The optical quality of the human eye in monochromatic light will be measured under comparable conditions with two techniques: an improved version of the laser interferometric technique of Campbell and Green (1965) and a variant of the double-pass technique of Campbell and Gubisch (1966). These techniques will be used to determine the off-axis image quality of the human eye, about which there is presently almost no information. 2) Techniques will be developed to form diffraction-limited images of the fundus without blurring by aberrations in the eye. The techniques will be adapted from recent breakthroughs in astronomical imaging that have made it possible to obtain crisp images of stars despite atmospheric turbulence, telescope aberrations, image motion, and small numbers of photons in the image. The techniques may provide improved images of fine structures such as the retinal nerve fiber layer, the microvasculature, and may even allow the cone mosaic to be resolved in the living human retina. These experiments will be performed in collaboration with G. Michael Morris and Doo Jin Cho of the Institute of Optics at the University of Rochester. 3) High resolution measurements will be made with laser interference fringes of the geometry of primate LGN receptive fields, including in some cases the number and packing arrangement of cones that feed the receptive field center. These measurements will establish the amount of neural convergence that occurs in the retina and LGN at each retinal eccentricity, undistorted by the optical quality of the eye. These experiments will be performed in collaboration with Peter Lennie, who is also at the Center for Visual Science.